The present disclosure generally relates to subterranean cementing operations. More particularly, the present disclosure relates to an apparatus for reverse circulation cementing of surface casing in subterranean formations and associated methods of use.
Cementing of a casing string is often accomplished by pumping a cement slurry down the inside of a tubing or a casing, and then back up the annular space around the casing. In this way, a cement slurry may be introduced into the annular space of the casing (e.g. the annular space between the casing to be cemented and the open hole or outer casing to which the casing is to be cemented). Such methods often are referred to as conventional circulation methods.
Though conventional circulation methods are the methods most commonly used for pumping cement compositions into well bores, these methods may be problematic in certain circumstances. For instance, a well bore may comprise one or more weak formations therein that may be unable to withstand the pressure commonly associated with conventional circulation cementing operations. The formation may breakdown under the hydrostatic pressure applied by the cement, thereby causing the cement to be lost into the subterranean formation. This may cause the undesirable loss of large amounts of cement into the subterranean formation. This problem may be referred to as “lost circulation” and the sections of the formation into which the fluid may be lost may be referred to as “lost circulation zones.” The loss of cement into the formation is undesirable, among other things, because of the expense associated with the cement lost into the formation. Likewise, high delivery pressures can cause the undesirable effect of inadvertently “floating” the casing string. That is, exposing the bottom hole of the well bore to high delivery pressures can, in some cases, cause the casing string to “float” upward. Moreover, the equivalent circulating density of the cement may be high, which may lead to problems, especially in formations with known weak or lost circulation zones.
Another method of cementing casing, sometimes referred to as reverse circulation cementing, involves introducing the cement slurry directly from the surface into the annular space rather than introducing the cement slurry down the casing string itself. In particular, reverse circulation cementing avoids the higher pressures necessary to lift the cement slurry up the annulus. Other disadvantages of having to pump the cement slurry all the way down the casing string and then up the annulus are that it requires a much longer duration of time than reverse circulation cementing. This increased job time is disadvantageous because of the additional costs associated with a longer duration cementing job. Moreover, the additional time required often necessitates a longer set delay time, which may require additional set retarders or other chemicals to be added to the cement slurry.
Typically, when cementing strings of casing, such as production casing or intermediate casing, a means of isolating the annulus is required to divert flowback of the cement up and out to the flowline. Such methods often require the use of conventional pack-off means such as a diverter or blowout preventers. Moreover, a volume based method is typically used, wherein the anticipated volume of cement needed to cement the casing string is calculated. The calculated volume may be doubled or even tripled in some instances and that amount of cement may be pumped into the formation to cement the casing string. This method causes excessive cement waste and costs affiliated with the volume of cement used.
Reverse circulation cementing of surface casing may pose certain obstacles as well. In the presence of only a conductor casing or in an open-hole, a diverter may need to be installed on a conductor casing prior to reverse circulation cementing a surface casing to isolate the annulus between a conductor casing and a surface casing. These structures are often complex and expensive, thus increasing the cost of completing the well. Moreover, in certain regions of the world, the number of diverters available for use in cementing operations may be unable to accommodate the demand for them. Thus, there is a need for a cost-effective and readily available means to isolate the annulus between a conductor casing and a surface casing for reverse circulation cementing of a surface casing.